Number Theory includes so many cool ideas. I especially like playing with modular arithmetic, and seeing the power it can have. I've never taken a number theory course myself, so I'm consolidating my thinking, and enjoying the stretching.
Here's a problem from the book (modified a bit):
I've got one part solved, and am still thinking about another part...Consider n! and the sum 1+2+...+n.
When is the sum a factor of the factorial?(problem 6.31)
[Please don't give complete solutions in the comments. But I'd love to know if you've played with it, and what approach you took.]
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